How thick to make the wall of a bowl depends on many things. How thick do you want to make it? The kind of wood you are using may determine how thin the bowl can be turned. Is the bowl functional or for display? The turner has to decide how thick the bowl should be and why it should be a certain thickness. Then the bowl should be turned to meet these criteria.

In general, utility bowls such as salad bowls or others made for functional use have thicker walls than bowls turned for exhibition. More important than wall thickness, however, is the form of the bowl, which should have pleasing lines flowing from the rim of the bowl to the foot. Wall thickness should be fairly uniform from the rim to the bottom of the bowl, but some turners prefer the wall to be slightly tapered, thinner at the top than at the bottom. Other turners prefer the opposite with the wall being a little heavier at the top than at the bottom. Take your pick. Most importantly the bowl should be well turned, properly sanded, and finished with the foot diameter appropriate for the size of the bowl.

If you want precise numbers for wall thicknesses, refer to this table taken from one of Ray Key’s excellent books. These ratios are usually applied to domestic bowls.

Measurements are a good guideline, but a statement from Ray Key summarizes the challenge of turning bowls, “We are back to spontaneity, that unmeasureable, undefinable quality that makes constant success so elusive! We will make good bowls often, special ones only rarely.”

The wood of choice for glue blocks generally depends on what scrap is available, but I usually choose a hardwood such as poplar, willow, or soft maple. Softwoods will also do the job, but I prefer hardwoods because of their ability to hold screws and their superior strength in general. I like to make the waste block from wood that has been jointed or planed; I don’t use rough stock. The surface of the bowl back to which the glue block will be glued should also be planed smooth and flat.

Assuming that both the bowl blank and the glue block are dry, I prefer to use an aliphatic resin glue such as Titebond, but any of the white woodworking glues will do just fine. Put a light coat of glue on both surfaces to be glued, rub the glue block into position, and clamp it lightly. This can be done by setting a weight on the glue block. Leave the assembly for several hours, preferably overnight in an area 60 degrees or warmer.

If a dry waste block needs to be glued to a blank which is not dry (15% or more moisture content), the best adhesive to use is a thick cyanoacrylate. Put the thick cyanoacrylate on one surface and spray an accelerator on the mating surface. Work quickly and accurately because the joint will set up almost instantly. If squeeze-out occurs, spray with accelerator to set it up. This bond will work, but it does not have the strength of the conventional aliphatic resin glues. The cyanoacrylate bond is also brittle and will not take a lot of impact, but if you want to glue dry wood to wet wood, it is the only choice.

Cyanoacrylate glue (superglue) is relatively new to the woodturner but will bond to a wide range of materials including wood, metal, and some plastics. They are available in thin, thick, and flexible formulas.

Thin glue can be used to bond hairline cracks, harden soft or punky areas in spalted wood, or bond bark to the edge of natural-edged bowls. In general, the thin glue will bond any area that cannot be separated then glued back together.

Thick glue is a gap-filling glue of syrupy consistency and is used for bonding separate pieces such as waste blocks to bowl blanks and pen tubes into pen blanks. This glue can be used to bond a waste block to an unseasoned bowl blank. However, when the roughed-out bowl blank dries, the waste block will usually partially separate from the roughed-out bowl. There are many variations to these glues, such as the flexible glue, which bonds much the same as the thick cyanoacrylate, but the bond is not so brittle and will allow for a little movement between two dissimilar materials without the joint failing.

For instant bonding, all the glues require an activator or hardener. A small spray from an activator bottle or an aerosol container can provide bonding in 30 seconds or less. However, water vapor in the air or moisture in the wood will also set the glue, but it may take a few minutes or several hours, depending on conditions.

For long-term storage, it is best to store unopened containers in the refrigerator or freezer. The material can be used once it has reached room temperature. Once the bottle has been opened, don’t return it to the refrigerator or freezer. These areas have high humidity levels which will speed up the setting of the glue in the bottle. Once the tip has been cut off and glue used, set the bottle down and tap it gently, allowing the glue to drain out of the tip and down into the bottle. At this point, the cap cover can be put on or left off; in my experience it doesn’t make much difference. If the tip doesn’t drain, however, the glue will harden in the tip.
There doesn’t seem to be any difficulty in gluing oily woods, such as cocobolo, as long as the surfaces are freshly machined and free from dust.

Wood is an organic material, so it is constantly taking in or giving up moisture. Minute changes in dimension are always occurring; therefore, laminated joints are always being stressed, particularly if end grain is glued to long grain. The glue will not deteriorate and cause joint failure, but other factors will contribute to joint failure.

The life of long-term glue-ups depends on the moisture content of the wood, temperature changes, changing humidity, if the woods have the same grain direction, etc. These are the same problems encountered when laminating with other glues, but cyanoacrylates set harder and are more brittle than white or aliphatic resin glues. Therefore the cyanoacrylates are less tolerant of wood movement and one can expect a higher rate of joint failure.

CAUTION: DO wear eye protection as these glues set instantly when in contact with the skin. Fingers will bond instantly, and eyes can be glued shut. Be careful!